This proposal explores physiological and molecular mechanisms by which 3 model carcinogens suppress keratinocyte differentiation in serially cultivated human squamous carcinoma cells. First, the action of the potent animal carcinogen and tumor promoter 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in suppressing accumulation of the particulate transglutaminase and the 56-58 kd keratins will be investigated. To test the hypothesis that this suppression is mediated by vitamin A as a consequence of TCDD antagonism of hydrocortisone action, the effect of TCDD on expression of transglutaminase and kertains will be measured in the absence of endogenous vitamin A. The influence of TCDD on retinol uptake and metabolism, levels of the cellular retinol binding and glucocorticoid receptor proteins and whether the suppression of differentiated function occurs at the transcriptional or translational level will then be studied. Second, the uncoupling of involucrin and particulate transglutaminase expression by benzo(a) pyrene will be investigated. This model carcinogen may arrest the cellular differentiation in what is ordinarily a transitory intermediate state. A limited survey of polycyclic aromatic hydrocarbons and related compounds will be undertaken to find whether this property is characteristic of inducers of aryl hydrocarbon hydroxylase. In addition, possible benzo(a)pyrene uncoupling of the differentiation program in normal human epidermal cells and a continuous line of premalignant human keratinocytes will be tested. Third, the phorbol ester promoter-mediated suppression of transglutaminase and involucrin will be investigated. This response will be characterized kinetically, and the activity of several structurally related and unrelated compounds examined. The role of diacylglycerol in governing the response, including possible generation of this activator of protein kinase C by physiological effectors, will be explored. The results may help to elucidate retinoid-glucocorticoid interactions influencing keratinocyte physiology and to resolve factors coordinating keratinocyte differentiation. Moreover, in furthering our physiological and molecular understanding of target cell response to carcinogens, this work may permit refinements in assessing human risk posed by environmental agents.